Core diameter measurement of graded-index multimode fibers by the side launch excitation technique

A new core diameter measurement technique using side launch excitation is presented. The core diameter of a factory length graded-index multimode fiber can be measured by this technique without cutting it down to a short length. The measurement error can be reduced to a sufficiently small value by optimally varying the K parameter, which determines the core diameter from the near-field intensity peak value. The discrepancy between the core diameters measured by the new method and those by the conventional transmitted near-field technique with uniform excitation, as recommended by CCITT, was found to be less than ±0.4 μm experimentally